The effect of defoliant application on yield and yield components of some cotton (Gossypium hirsutum L.) cultivars at timely and late sowing

This study was aimed to assess the effect of defoliant application on yield and yield components of some cotton cultivars at timely and late sowing under Harran Plain conditions in 2017 and 2018 growing seasons. Field trials were arranged employing randomized blocks split-split plots design with 3 replications. In the study, sowing times (i.e.10th of May and 10th of June) consisted the main plots, cultivars (i.e. Candia and Lima) placed in the sub-plots and defoliant applications (i.e. Control and Dropp Ultra (600 ml ha-1)) were in the sub-subplots. Each plot was sown with a length of 12 m and 6 rows, with a 70 cm inter-row and 15 cm intra-row spacing. In the trials, the defoliant chemical called Dropp Ultra (i.e.120 g Thidiazuron + 60 g Diuron) was used. The application was practiced when the 60 % of boll opened. It was found that Candia and Lima cotton cultivars sown timely gave seed cotton yields of 5296.7 and 5073.3 kg ha-1 respectively, whereas at late sowing gave the seed cotton yields of 4672.5 kg ha-1 and 4545.8 kg ha-1in 2017 and 2018; Candia gave the higher seed cotton yield (i.e. 5179.2 in 2017 and 5013.3 kg ha-1 in 2018) than Lima cultivar (i.e. 4790.0 in 2017 and 4605.8 kg ha-1 in 2018) in both years. Results indicated that that the defoliant application increased the seed cotton yield comparing control plots. Defoliant application positively influenced the seed cotton yield (kg ha-1), plant height (cm), number of opened bolls (per plant-1), boll weight (g) and boll seed cotton weight (g). However, there were no significant effects on the number of bolls (per plant-1) and 100 seed weight (g). It was concluded that defoliant application and timely sowing can be recommended for farmers in the region.